JP 2008-238921A discloses a damper control device that controls a damping force of a damper interposed between a sprung member and an unsprung member of a vehicle. The damper control device estimates a condition of a road surface on which the vehicle is running from an effective value of vibration of the sprung member in a sprung resonant frequency range, an effective value of vibration of the sprung member in an unsprung resonant frequency range, and an effective value of vibration of the sprung member in an intermediate frequency range between the sprung resonant frequencies and unsprung resonant frequencies. The damper control device causes the damper to output a damping force suitable for the estimated road surface condition.
Such a damper control device is capable of determining the road surface condition, and therefore improving the ride quality of the vehicle by causing the damper to generate a damping force suitable for the road surface condition.